Beryllium has many properties that make it desirable for use in severe environments. Such properties include low density, good thermal conductivity, good infrared reflectivity, high stiffness, low coefficient of thermal expansion at cryogenic temperatures, and small nuclear cross section. However, the high toxicity of beryllium powders has minimized its use. In addition, superpolished beryllium surfaces tend to lose their low scatter quality due to oxidation. Beryllium also has a relatively high porosity, which can result in deleterious voids and etches forming on the finished product.
As a result of the foregoing drawbacks, when high strength silicon carbide (SiC) has been used in lieu of beryllium, it has demonstrated considerable advantages and much success in severe environment applications. It exhibits excellent oxidation and creep resistance, and is believed to outperform beryllium in many if not all applications. For many applications including hard disk drive, super conductor wafer applications and high-reflective optics, superpolished surfaces are required.
Conventional polishing techniques are capable of producing a polished surface having a surface roughness on the order of about 100 .ANG. RMS (random measurement sampling). However, decreased surface roughness has obvious advantages depending on the application. For example, in computer hard disk drive applications, surface roughness less than 10 .ANG. RMS would allow substantially more information per disk area. Similarly, in laser application, a 10 .ANG. RMS mirror surface would allow for more efficient operation by creating higher laser reflectivity (therefore lower laser absorption), thus lessening the possibility of mirror burns.
Accordingly, there exists a need for producing hard ceramic materials having superpolished surfaces with a surface roughness below about 20 .ANG. RMS, and indeed, as low as about 0.5 .ANG. RMS even with substrate diameters of 10-12 inches or larger.